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Mystery Rock / Fossil Help


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I found this on the Olympic Peninsula of Wa State along a rivers edge. i found it so interesting, but could never figure out what it is or how so many things ended up in the same rock. I have no idea if there are any fossils here and would appreciate any suggests. I can take more photos if there are areas of interest. Thanks.

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It's certainly a conglomerate, but some material on the exposed surface hint of concretion and ordinary stone. Some of the material (pea gravel size) resemble some fossil material and maybe bone fragments. I found something similar near Seiku long ago, had a shrimp claw concretion inside.

Anyone who has never made a mistake has never tried anything new.
-Albert Einstein


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Interesting responses.

When you say conglomerate, does that indicate it may be man made? I was wondering about that asphalt colored black stone being man made.

One of the round items has concentric rings. Any suggestions on how that occurs?

Whether fossil, rock or ?, I am fascinated whenever I look at it.


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This really is a terrific geological specimen!

Simply put, conglomerates are formed when erosion concentrates and mixes loose material when then coalesce as a solid structure. The fun comes when you try to deduce the histories of the component pieces. The stream-worn boulders went through a very different set of circumstances than the sharp chips, obviously, and to tease out their possible origins, you begin by asking what they are made of and sleuthing out the source deposit. The full picture can span many geologic eras, with sedimentary, metamorphic, and igneous material all represented within the paleo oleo. :)

"There has been an alarming increase in the number of things I know nothing about." - Ashleigh Ellwood Brilliant

“Try to learn something about everything and everything about something.” - Thomas Henry Huxley

>Paleontology is an evolving science.

>May your wonders never cease!

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Yes, it is a great specimen and certainly not man-made.

First off, it’s what’s known as “matrix-supported” (ie it’s the finer stuff holding it together), defined as a “paraconglomerate” when more than 15% of it consists of grains smaller than 2mm.

Secondly, it’s what’s known as “polymict” (ie it contains clasts of many different lithologies.) A clast is a larger fragment of rock contained in a finer matrix.

Thirdly, it’s likely “extraformational” (ie the clasts are derived from rocks which are older than the formation in which the conglomerate was found).

Fourthly, it’s “cobble conglomerate” (ie the clasts are generally beyond 64mm in size but less than 256mm).

Fifth, its “poorly sorted” (ie it contains a variety of sizes of clasts which are a mixture of angular fragments and smoothed rocks.)

Typically, those features might well arise from glacial deposition – in which case we would term the rock “tillite”. That’s what I would have said it was, were it not for the fact that there are no recognised deposits of tillite in Washington State. It might well have been glacially transported to where you found it and it could therefore be a chunk of tillite from an area outside Washington State, in which case we would term it an “erratic”.

I think it's more likely what is known as “basal” conglomerate – normally laid down in deep marine environments and representative of an ancient shoreline at the time. You might be able to see fossil debris in it (broken shell pieces etc) if that is the case.


I keep six honest serving-men (they taught me all I knew);Their names are What and Why and When and How and Where and Who [Rudyard Kipling]

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very interesting piece, thanks for such a thorough explanation Roger :)

"Your serpent of Egypt is bred now of your mud by the operation of your sun; so is your crocodile." Lepidus

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WOW! Nice explaination.

"Absence of evidence is not evidence of absence"_ Carl Sagen

No trees were killed in this posting......however, many innocent electrons were diverted from where they originally intended to go.

" I think, therefore I collect fossils." _ Me

"When you have eliminated the impossible, whatever remains, however improbable, must be the truth."__S. Holmes

"can't we all just get along?" Jack Nicholson from Mars Attacks

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Very helpful and well written information! I'm so glad I put in the photo and found such a great forum community. The more I learn the more fascinated I become. Tomorrow I'll be looking at it with a magnifying glass!

I'm now starting to understand how so many different things could end up in one piece.

I'm particularly taken with the possibility (as mentioned by painshill) of it being from somewhere other than WA State and finding it's way here!

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What part of the Olympic Pen did you find that - near the north shore perchance?

We have similar material across from you here on Van. Island, on the beach near Sooke, which is Tertiary (Oligocene) and contains fossils, though I'm not sure I recognize those larger layered chunks.

PS if you could provide some larger form of those pics it would help.

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